For many years, conventional wisdom declared that no protein translation occurs in the axons of mammalian neurons. Instead all proteins needed for axonal functions were supposed to be synthesized in the cell bodies and shipped out to the axons. More recently, accumulating data has provided evidence that many mRNAs are found in axons in the mammalian nervous system. Evidence indicating that local translation in axons may be regulated by electrical activity, neurotrophic factors, and stress, have led to the hypothesis that axonal translation is particularly important for plasticity during learning, or in response to environmental stressors. In support of this idea, defects in local translation have been linked to Fragile X syndrome, which causes cognitive problems and autistic behaviors, and paraneoplastic disorders, which cause encephalitis in some patients with lung cancers. However, the mechanisms regulating local translation, and why defects in local translation lead to neuro-psychiatric dysfunction, are not understood. In part, this reflects the inadequacy of current approaches for analyzing local protein synthesis or identifying biological functions that rely on regulated local translation. To address this problem we initiated a collaboration with Michael Lin. Michael recently developed a technique called timeSTAMP, to identify proteins that are translated at a particular time period (4). We are working with Michael to modify this approach so it can be used for spaceSTAMP, to tag proteins translated in a particular location, and follow them over time and space. The goal of this proposal is develop the spaceSTAMP approach and use it to ask: Is there regulated local translation in axons? Are such locally translated proteins functionally important? Are locally translated proteins restricted to the axonal compartment, or do they facilitate communication between axonal terminals and remote portions of the neuronal cell body? These studies will develop and test a spaceSTAMP technique that allows one to tag proteins synthesized in axons, and to follow these components in time and space. This approach can then be used by the scientific community to solve problems such as the functional importance of the fragile X gene product, and ways in which activity or neurotrophin regulated translation contribute to neuro-psychiatric disorders.